The constructive innovation of the Franklin Street building earned it a place in the history of architecture. It was indeed the first time that Perret had experimented with the technique of reinforced concrete, which he would then use for the Champs-Élysées theater (1914), Notre-Dame du Raincy church (1922) and the national museum of Public works (1937). But the renown of this building is also based on other innovations: from a stylistic point of view, it is often considered a precursor of modernism, and Siegfried Giedion saw the first example of free plan. The masonry bearing the façade wall, punctuated with projecting windows, disappears on the ground floor and at the roof level, replaced by a window and a roof terrace. The U-shaped plan, concave on the street, transports the skylight to the front, allowing the rooms of the same apartment to have seen each other. The building thus significantly reinterprets the Parisian apartment building built between two adjoining walls. Above the shops on the lower two levels and including a mezzanine, each of the upper floors hosts a single apartment. The U-shaped plan pushes stairs, elevators, bathrooms and toilets to the back, living rooms overlooking the street. The kitchen is leaned against a common wall, near the service staircase. The three main pieces, in a row, are arranged symmetrically, in the center of the plane; the living room, in the middle, is entirely glazed and devoid of chimney, the sight on Paris becoming the main point of attraction. One floor includes two balconies on the street, a plan that has been modified to the upper levels, where recesses form rooftop terraces. In the seventh, the lounge is set back to make room for a balcony that occupies the entire width of the building. Through the terrace of the ninth floor apartment – the smallest of all – one ladder leads to the rooftop terrace and another to a terrace on the eighth floor, inaccessible from the service rooms at this level. . The design of the apartments – high ceilings, large glazed areas and balconies – reflects a new way of thinking the building, focusing not on the interior but on the light and outdoor space.